Many psychiatric disorders, including drug abuse, are characterized by behavior that is deemed "impulsive." Impulsivity is often defined as the choice for a small, immediate outcome or reinforcer over a larger, more delayed outcome, the self-controlled choice. Impulsive choices may be a result of the value of the larger reinforcer being discounted due to the delay to its presentation. Drug abusers have been shown to discount the value of delayed outcomes to a greater extent than non-drug abusers. However, it is not clear whether delay discounting or impulsive choice is an acute drug effect, a consequence of long-term drug exposure, or a pre-existing component of an individual's behavioral repertoire determined by behavioral history or genetics. The present proposal is designed to begin to address these issues by the investigation of acute and chronic effects of drugs of abuse on impulsive choice in an animal model using two different rat strains, Lewis and Fischer 344, which differ in potentially relevant neurochemical and behavioral measures. The research has two Specific Aims that are addressed in two series of experiments. Specific Aim 1 is to investigate acute effects of drugs of abuse on impulsive choice in the two rat strains, which are expected to differ in their impulsive choices. Specific Aim 2 is to examine effects of repeated administration (long-term exposure) of drugs of abuse on impulsive choice in the two rat stains. Differential and systematic findings in impulsive choice and drug effects will lay the foundation for further studies into understanding the role of neurochemistry and genetics into delay discounting and impulsive choice. The proposed research will contribute to the understanding of the neurobehavioral biology of delay discounting and impulsive choice and effects of drugs of abuse. Ultimately, this work may have relevance to many disorders characterized by impulsive behavior such as, drug abuse, gambling, violence, ADHD, and other risky behaviors, e.g., sharing needles that may result in the spread of HIV/AIDS. [unreadable] [unreadable] [unreadable]